A large variety of materials and compositions has been employed for the topical treatment of skin conditions caused by drying, photodamage, aging, acne and the like. In addition to being effective and safe, any product used for the treatment of skin conditions should be convenient to formulate, easy to use, have long term stability, and be easy to handle. Additionally, such products should preferably be low in cost.
Retinoic acid, and other retinoid compounds are effective for treating acne, wrinkles and other skin conditions. However, these materials can be very toxic and must be used under close medical supervision, and hence are prescription medications. In addition, retinoids are expensive. Strongly corrosive materials such as phenol, mineral acids and halocarboxylic acids such as trichloroacetic acid have also been used to treat damaged skin. Such corrosive materials achieve a therapeutical effect by causing the outer layers of skin to peel away. These materials must also be used under medical supervision since they can produce serious damage if misapplied.
A number of formulations have been developed for dermatological preparations, using alpha hydroxy acids and alpha keto acids. These acids are used at fairly high concentrations, in clinical settings, to produce superficial peeling of the skin. They are also used at lower concentrations by consumers and paraprofessionals to smooth and condition the skin and reduce wrinkles. In many instances, these materials can still be irritating, and as a result, compositions have been developed wherein buffering agents such as amphoteric compounds or alkaline materials have been added to the acids to raise their pH. Such compositions are shown in U.S. Pat. Nos. 4,105,782; 4,105,783 and 5,091,171. In other instances, skin care compositions have been formulated utilizing ascorbic acid, and such compositions are shown in U.S. Pat. Nos. 4,983,382 and 5,140,043.
In yet other instances, skin care compositions have been prepared utilizing relatively neutral species such as salts. PCT Patent Application WO96/19182 discloses the use of inorganic salts, primarily of magnesium, manganese and various lanthanide elements, for reducing skin irritation. U.S. Pat. No. 5,478,560 discloses the use of salts of mixed amines for treating dry skin.
In addition, skin lightening compounds are included in skin care compositions to treat conditions such as uneven skin color, hyperpigmentation, freckling, age spots, darkening associated with birth control pills and pregnancy, and pigmented scaring. In particular, hydroquinone is effective in bleaching affected areas. However, skin treatment formulations containing hydroquinone darken over time, decreasing the potency of the composition and rendering the product unattractive and unappealing to consumers.
As can be seen, there is a very large body of prior art directed to topical treatments for various dermatological conditions. The efficacy and safety of the various prior art compositions vary widely as do the cost and ease of formulating and using the compositions. Thus, there is still a need for a composition for treating dermatological conditions, which composition is effective, safe, easy to formulate and use, low in cost, stable and attractive to a consumer.
Certain amino acids are beneficial compounds for the treatment of skin conditions. Particularly preferred are the alpha amino acids; that is to say, those amino acids in which the amine group is alpha to the carboxylic acid. These alpha amino acids are also referred to herein as “acidic amino acids” or “amino fruit acids. One particularly preferred group of acidic amino acids comprises dicarboxylic amino acids. Various acids, including carboxylic acids, solubilize the amino acids so as to facilitate their incorporation into various dermatological compositions. Further, when acidic amino acids are solubilized with carboxylic acids, a beneficial interaction occurs which creates a new therapeutic species generally referred to herein as “a carboxylated, amino fruit acid” or a “tricarboxylic acid.” Both alpha amino acids and carboxylated acidic amino acids are highly effective for treating a variety of skin conditions. The materials have a strong antioxidant action is very non-caustic to skin even at very low pH levels. Further, these materials have now been found to inhibit darkening of hydroquinone-containing formulations. As will be described hereinbelow, the present invention provides a stable composition which has very good utility for treating skin conditions associated with dryness, aging, photodamage such as photopigmentation and keratoses as well as acne and seborrheic keratoses. These and other advantages of the present invention will be apparent from the discussion and description which follow.